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Full text of "The Cambridge Natural History"

contrary to the prevailing superstition, it is not domestic animals
which show the greatest amount of tooth variation. As to special
homologies between tooth and tooth, with which we shall deal
on a later page, Mr. Bateson has urged almost insuperable
difficulties.

The   teeth   of the   Mammalia   are   almost   without   exception
" heterodoiit," i.e. they show   differences of  structure   in   different

FIG. 34.—Skull of Dasyurus (lateral view). al.spJi, Alisphenoid ; a-ng, angular process
of mandible ; jfr, frontal ; Jit, jugal ; Zcr, lachrymal ; mace, maxilla ; nas9 nasal ;
oc.cond,.occipital con.dyle ; par, parietal; par.oc, paroccipital process; p.max,
preniaxilla ; s.oc, snpraoccipital ; sg, sqxiamosal ; sq', zygoniatic process of sojua-
xuosal. (From. Parker and Has well's Zoology.')

parts   of the mouth.     As a   general   rule, teeth can  be  grouped
into  cutting  incisors,  sharp  conical  canines, and   molars, with   a

FIG. 35.—Upper and lower teeth of one side of the moxith of a Dolphin (LagenorJit/n-
chus\ illustrating the homodont type of dentition in a mammal. (After Flower
and Lydekker.)
surface which is in the majority of cases suited for grinding. In
this they contrast with the majority of the lower vertebrates,
where the teeth are " homodont" (or, better, Jiomoeodonf), i.e. all
more or less similar and not fitted by change of form to perform
different duties. But there are exceptions on both sides. In